A multidisciplinary study of renal disease in children and experimental rat models encompassing a study of the control of C3 biosynthesis in human monocytes; the investigation of the idiotypic determinants of the C3 nephritic factor which has been identified as an immuniglobulin, a specific antibody to C3bBb. C1 biosynthesis by normal and malignant transitional epithelium is being studied as a potentially useful marker of renal tract malignancy. The ultrastructural lesion of autologous immune complex nephritis is being compared in Munich-Wistar rats and Lewis rats. The composition of cryoglobulins in acute post-streptococcal glomerulonephritis revealed the presence of almost exclusively IgG in comparison with SLE cryoglobulins. Comparison of hyporesponder strains (DFA/2 rats) with normal responders (Lewis rats) to proximal tubular antigen vealed genetic control of variant suppressor function. Chemical modification of the antigen overcame suppressor differences. The characterization of the suppressor cells is being studied.